Ion implanters are well known and have been used for many years in the field of semiconductor manufacturing to modify workpieces such as silicon wafers. In simplest terms, these complex systems generate an ion beam that is directed to the wafer for selectively doping the wafer with impurities of controlled concentration and energy, thereby yielding a semiconductor material that forms the foundation for the fabrication of an integrated circuit or a so-called microchip.
A typical ion implanter includes: an ion source; an ion extraction electrode subsystem, a mass analysis device; a beam transport assembly; and a wafer processing station. The ion source typically encompasses a chamber for receiving a dopant material and generating ions of desired atomic or molecular dopant species therefrom. These ions are extracted from the chamber via an extraction member, which typically defines an extraction aperture operating in conjunction with the extraction electrode subsystem, which includes a set of electrodes that energize and direct the flow of ions out of the ion source chamber through the extraction aperture. The desired dopant ions are then separated from other ions and byproducts of the ion source in a mass analysis device, typically a magnetic dipole, performing mass dispersion of the extracted ion beam. The beam transport assembly includes a vacuum system containing a number of various electrostatic and/or magnetic focusing, filtering and acceleration/deceleration components for transporting the ion beam to the wafer processing station while creating and/or maintaining desired properties of the ion beam. Finally, the transported ion beam impinges on wafers that are transferred into and out of the wafer processing station to implant ions from the ion beam into the wafer.
Ion sources that generate the ions used to create the ion beam are well known. For example, commonly assigned U.S. Pat. No. 5,420,415 to Trueira and U.S. Pat. No. 5,497,006 to Sferlazzo et al describe various aspects and details of a typical “Bernas-type” ion source used to generate ions in semiconductor manufacturing equipment. While the contents of the '415 and '006 patents are incorporated herein by reference for all purposes, it will be understood that the present invention can be applied to other types of ion sources, including but not limited to, so-called “Freeman-type” ion sources as well as RF based ion sources used for extracting ion beams.
As previously noted, an ion source typically comprises a chamber, sometimes called: a gas confinement chamber; an arc chamber; or a plasma chamber, which is made up of conductive chamber walls that bound an ionization region. A gas supply is positioned in communication with the gas confinement chamber for delivering an ionizable gas thereto (or for housing a sputterable ionization material therein), as is well known in the art. An electron source is situated with respect to the gas confinement chamber for emitting ionizing electrons into the gas ionization region. In a typical “internally heated cathode” based ion source, a heated cathode is provided in the form of a filament supported inside a conductive body for heating the cathode and causing ionizing electrons to be emitted into the gas confinement chamber.
The gas confinement chamber includes an extraction member defining an extraction aperture, or so-called arc slit for allowing ions to exit the chamber. The gas confinement chamber and extraction aperture are positioned relative to the extraction subsystem so as to create a well-defined ion beam from the ions extracted from and exiting the gas confinement chamber. Thus, ions created within the chamber interior are drawn toward the extraction member and are transported through the extraction aperture to form the ion beam. The extraction aperture may be in the form of an elongated opening or through hole formed in the extraction member. Commonly assigned U.S. Pat. No. 7,453,074, also incorporated by reference herein, discloses that it may be desirable to vary the size and/or shape of the extraction aperture to define different ion beam profiles and/or to vary the ion source operation and various characteristics thereof.